1. Field of the Invention
The present invention relates to a magneto-optical recording apparatus which irradiates a magneto-optical recording medium with a laser beam and applies a modulation magnetic field to the side of the medium opposite to the irradiation side thereof to conduct magneto-optical information recording.
2. Related Background Art
In the magneto-optical recording apparatus of this type, information recording is performed as follows. A laser beam emitted from a semiconductor laser is converged by an optical head into a beam spot of a diameter of about 1 .mu.m to irradiate, for example, a magneto-optical recording medium in the form of a disk, and an external modulation magnetic field is applied at a position corresponding to the irradiation position through a magnetic head in a direction normal to the magneto-optical recording medium.
A main part of such a magneto-optical recording apparatus is structured, for example, as shown in FIG. 1. There is a recording layer 2 of a vertical magnetization film in the upper portion of the disk magneto-optical recording medium 1. A magnetic head 3 is disposed to face the recording layer 2 above the magneto-optical recording medium 1 and is movable in a tracking direction. Further, an optical head 4 is disposed to face the magnetic head 3 below the magneto-optical recording medium 1 and is movable in the tracking direction and in a focusing direction.
The magnetic head 3 is constituted by a U-shaped core 5, which is made of a magnetic material with a high permeability, for example, a sintered ferrite material, a coil 6 wound around a main pole portion of the core 5, and a slider 7 for floating to hold the magnetic head 3 with a slight gap between it and a surface of the magneto-optical recording medium. The slider 7 is made, for example, of a non-magnetic material such as a ceramic.
In an information recording operation, while the recording medium 1 is rotated at a high speed, a laser beam from the optical head 4 is converged into a beam spot b of a diameter of about 1 .mu.m to irradiate the recording layer 2 so as to heat a portion thus irradiated. An electric current modulated by an information signal is supplied to the coil 6 on the magnetic head 3 to excite the core 5. Then, a vertical magnetic field c along a direction of magnetization at that moment is applied to the vicinity of the beam spot b on the recording layer from the main pole portion 5p of the core 5.
However, when the information recording operation is carried out by using the above magnetic head, the magnetic head has a high heating characteristic due to the material of the core generating a bias magnetic field, that is, due to a high-frequency loss peculiar to the magnetic material. The heating itself may possibly deteriorate the magnetic properties and other properties, and will negatively affect the facing recording layer of the magneto-optical recording medium. In detail, in the case where the core of the magnetic head is made of a polycrystal Mn-Zn ferrite material, a peculiar loss is seen if the core is excited at a high frequency. As a result, the core heats up and causes a change in magnetic properties, for example, a decrease in permeability, and a decrease in saturation magnetic flux density, so that a magnetic field of sufficient strength may not be applied, which results in a failure to provide good signal recording. Also, a thermal, negative effect is a deformation of the magneto-optical recording medium. On the other hand, if the frequency of the information signal is decreased in order to avoid these problems, then the transfer speed of the information signal cannot be increased, which is contrary to the desired high speed processing.
Further, in order to obtain a magnetic field of sufficient strength applied using the above magnetic head, a relatively large electric current, for example, three to five times the amount of electric current applied to a magnetic head used for a hard disk, must be supplied to the coil 6. Hence, there is a problem in that it requires an increase in dissipation power of a drive circuit supplying the electric current to the coil 6. The supply of such a large electric current restricts the upper limit of the recording frequency in the designing of the drive circuit for the magnetic head, which prevents an increase in the recording speed of an information signal.